1. Field of the Invention
The present invention relates to a method for interfacing between a cellular telephone and a personal data assistant (PDA) in a radio multi-terminal communications system, and in particular, to a data synchronizing method and system for allowing a cellular telephone and a PDA to share data.
2. Description of the Related Art
FIG. 1 shows a block diagram of a radio multi-terminal communications system which is divided into a cellular telephone 200, being a first communication terminal, and a personal data assistant (hereinafter called PDA) 100, being a second communication terminal.
First, as for the cellular telephone 200, a second CPU (Central Processing Unit) 211 controls the overall operations of the cellular telephone 200 and communicates with a first CPU 111 in the PDA 100. A program memory 212, being a flash memory, stores a control program of the second CPU 211. A data memory 213, being a RAM (Random Access Memory), temporarily stores data generated during operations of the cellular telephone 200. A nonvolatile memory 214, being an EEPROM (Electrically Erasable and Programmable Read Only Memory), stores telephone numbers registered for abbreviated dialing (or speed dialing) and system parameters. A keypad 215 generates command key signals for controlling the second CPU 211 and key signals for inputting data. A display 216, under the control of the second CPU 211, displays state information generated during operations of the cellular telephone 200. An LCD (Liquid Crystal Display) may be used for the display 216.
In addition, the cellular telephone 200 includes a communication module including an RF (Radio Frequency) interface 217, a frequency converter 218, a MODEM (Modulator-Demodulator) 219, and a signal processor 220. The communication module is controlled by the second CPU 211. The signal processor 220 is composed of an interleaver and encoder, a deinterleaver and decoder, a vocoder, and a PCM CODEC (Pulse Code Modulation Coder-Decoder).
Here, it should be noted that the communication module is missing a transmission part and a reception part, omitted as a matter of convenience. Further, FIG. 1 is missing control signal lines for the second CPU 211, a voice signal processor, and a transceiver, also omitted as a matter of convenience.
During a transmission mode, the signal processor 220 encodes transmission data, and the MODEM 219 modulates the encoded transmission data. The frequency converter 218 up-converts the modulated transmission signal to a transmission frequency band, and the RF interface 217 filters the RF transmission signal output from the frequency converter 218 to pass the transmission band frequency signals only. Further, the RF interface 217 amplifies the transmission signals and radiates the amplified transmission signals to the air via an antenna.
During a reception mode, the RF interface 217 low-noise-amplifies the low power RF signals received via the antenna and filters them to pass the reception band frequency signals only. The frequency converter 218 down-converts the received RF signals to the baseband signal, and the MODEM 219 demodulates the output signals of the frequency converter 218.
Next, as for the PDA 100, the first CPU 111 controls the overall operations of the PDA 100 and communicates with the second CPU 211 in the cellular telephone 200. A program memory 112, being a flash memory, stores a control program of the first CPU 111. A data memory 113, being a RAM, temporarily stores data generated during operations of the PDA 100 under the control of the first CPU 111. A nonvolatile memory 114, being an EEPROM, stores information input by the user and information received from the cellular telephone 200. A keypad 115 generates command key signals for controlling the first CPU 111 and key signals for inputting data. A display 116, composed of an LCD, displays the status information generated during operations of the PDA 100 under the control of the first CPU 111. A communication module 117 forms a data communication channel between the PDA 100 and the cellular telephone 200 by way of an UART (Universal Asynchronous Receiver Transmitter) 150.
For instance, the cellular telephone 200 may be a CDMA (Code Division Multiple Access) terminal and the PDA 100 may be a hand-held computer such as a notebook computer.
As illustrated in FIG. 1, in the radio multi-terminal communications system, the first CPU 111 in the PDA 100 asynchronously communicates with the second CPU 211 in the cellular telephone 200 by way of the UART 150. Here, the message transmitted therebetween has an HDLC (High-level Data Link Control) format and a transfer rate of 57.6 Kbps. The UART 150 is an asynchronous transceiver with serial-to-parallel and parallel-to-serial conversion functions, for transmitting data. With this combination, the PDA 100 can graphically process user interface data input from the cellular telephone 200.
As described, the radio multi-terminal communications system transmits data in the asynchronous simplified HDLC format in order to allow the cellular telephone 200 and the PDA 100 to share the data. Conventionally, upon occurrence of an event, the cellular telephone 200 and the PDA 100 interchange data to share it, thereby providing a real time service to the user. However, such a data communication method leads to a reduction in the operating time (or run-time) of a battery. To save the battery, the system may transmit the data upon request of the user. However, in such a case, the system cannot provide the real time service.